Aluminum-beryllium alloys are finding application in components where low weight and strength are at a premium. For example, aluminum-beryllium alloys are finding use in the F22 fighter aircraft in the place of aluminum alloy components. The aluminum-beryllium alloys may, for example, consist of 20%, 40%, 60% beryllium by weight with the balance being aluminum. One popular alloy is AlBeMet AM162, which is 62% by weight beryllium and 38% by weight aluminum. These and similar aluminum-beryllium alloys have low weight, high stiffness, high thermal transfer, a low coefficient of thermal expansion, high heat capacitance, a high fatigue strength and good corrosion protection.
The industry presently uses the same processes for the brazing of aluminum-beryllium alloy parts as it uses for aluminum parts. However, problems have occurred with respect to the reliability and strength of junctions made with conventional aluminum brazing processes. Aluminum-beryllium alloys tend to form adherent, tenacious oxide surface films when heated to brazing temperatures--even at the very low pressures subsisting in vacuum brazing processes. These oxide films prevent the aluminum brazing alloys from wetting the aluminum-beryllium alloy surfaces resulting in inconsistent joints. Further, in jobs requiting the brazing of aluminum-beryllium alloy with aluminum, the brazing temperature must be held below the melting temperature of the aluminum or aluminum alloy being used. One method that has been tried to alleviate these problems is to populate the surfaces to be joined by brazing by subjecting the surfaces to an acid bath such as a nitric acid/sulfuric acid solution, but this has not worked. To date, the brazing of aluminum-beryllium alloys with this or unmodified aluminum brazing techniques has proven to be less than satisfactory. A need therefore exists for a brazing technique which will give strong bonds between brazed parts and a high degree of reliability.